In a machine, such as a motor grader, for example, an engine and a transmission work together to propel the machine and operate implements, such as a motor grader blade. A gear shift lever is used to select a gear for operating the machine from among a number of forward and reverse gears. Because motor graders are used for grading operations, they often work in loose materials which give rise to poor traction conditions. Poor traction conditions can cause the wheels to slip which is undesirable. Because the drive wheels are differentially geared, when one wheel loses traction, its wheel speed increases and the differential system may experience an overspeed condition. Accordingly, it will be appreciated that it will be highly desirable to controllably respond to slip by controlling engine and transmission speed or by limiting differential gearing.